Russian President Vladimir Putin, left, gestures while speaking to Chinese President Xi Jinping during the Shanghai Cooperation Organization (SCO) summit in Samarkand, Uzbekistan, Sept. 16, 2022.Sergei Bobylev, Sputnik, Kremlin Pool Photo/Associated Press, FileChina has been a key ally and crucial trade partner to Russia during the war in Ukraine.Cold War historian Sergey Radchenko argued in a New York Times op-ed that it's unwise for Putin to rely on China.Radchenko said history shows China will flip on allies as needed if it's to their benefit.As much of the Western world has shunned Russia over its invasion of Ukraine, China has served as the country's most powerful ally — but relying too heavily on that partnership could spell trouble for Russian President Vladimir Putin down the line.Putin and Chinese President Xi Jinping have boasted about their "no limits" friendship, driven in part by a desire to curb US power.